1. Field of the Invention
The present invention relates to a technique for positively controlling the tension of pile warp yarns on a pile loom in connection with the terry motion.
2. Description of the Prior Art
The applicant of this patent application has proposed a "Let-off Motion for a Loom" in Japanese Patent Application No. 61-268317 published as Japanese Publication No. 63-120141. This proposed let-off motion has a tension control system and a speed control system, and uses the speed control system in letting off pile warp yarns. In forming pile, the control system is changed over from the tension control system to the speed control system, and the tension roll is displaced to let off the pile warp yarns rapidly at a low tension. Consequently, loops having a predetermined length are reliably formed without omitting any loop.
In a pile loom of a moving cloth type, for example, since the warp yarns are slack while the control system is in a speed control mode in which pile warp yarns are let off rapidly at low tension, the tension of the warp yarns changes sharply in changing the control mode of the control system from a speed control mode to a tension control mode in which tension is closely regulated. Consequently, the performance of the tension control system becomes unstable temporarily due to the variation of the load after the control mode of the control system has been changed over from the speed control mode to the tension control mode. That is, the tension regulating operation of the tension control system for adjusting the warp tension to a desired value fluctuates temporarily and thereby the warp tension is caused to fluctuate about the desired value.
Furthermore, in moving the cloth fell backward to the beating position for tension control, the tension roller tends to move backward by inertia beyond a position where the tension roller should be stopped, so that the control operation of the control system fluctuates temporarily and becomes unstable. Such problems arise also in a pile loom of a moving reed type, such as a sword-beat type or a reed-beat type.
Such unstable performance of the control system is undesirable and will affect adversely to the construction of the pile.